The present invention involves the continuous production of rubber strip material impressed with a surface design and, more particularly, to an apparatus for the molding of a continuous strip of uncured or partially cured rubber with a design, such as a tire tread, and the curing thereof after removal from the mold.
Presently, tire treads, such as are employed in retreading worn tires, are made for the most part by simultaneously shaping and heat curing rubber compounds in a mold. The rubber stock is kept in the mold under pressure for essentially the entire curing period, since premature removal may cause so-called "blowing of the stock", that is, formation of numerous small voids caused by expansion of water and gases generated during the curing process. High pressures and long molding times of over 15 minutes are generally required to prepare a tread of good quality. As a result, this process has been essentially discontinuous, that is, the treads have been made in individual sections one at a time. Even when the process has been made continuous using cooperating endless belt molds with the rubber in strip form, such as disclosed, for example, in U.S. Pat. Nos. 3,214,792, 3,827,846 and Ger. GM 71 10 999, it has been found to be comparatively time-consuming.
Attempts at using more rapid radiation curing of the tire thread rubber, such as suggested, for example, in U.S. Pat. Nos. 1,906,402, 2,933,441, and 3,959,053, have not been entirely successful. It has been throught impractical to completely cure such treads by radiation, as it would require an exposure of the rubber stock while traveling in the mold. Penetration of the mold, which is usually made from steel, would necessitate the use of gamma rays, and as commercial sources produce gamma rays only at moderately low intensities, very long tread cure times would be required.